Occurrence of an External Spermatophoric Mass in the Spiny Lobster, Palinurus Gilchristi (Decapoda, Palinuridea)

Abstract

Within the family Palinuridae, external fertilization is only known to occur in the genus Panulirus in which the conspicuous spermatophoric mass with a hard protective matrix is well known. External spermatophores have not been recorded in other palinurid genera. In the course of examination of a sample of Palinurus gilchristi Stebbing, 1900, trawled off the Natal coast, five females were found to have spermatophoric masses on their thoracic sterna, indicating that external fertilization occurs in this genus. The spermatophoric mass was complete in only one specimen which was in a state immediately prior to oviposition. In the other specimens oviposition had just occurred and the spermatophoric masses were fragmented, presumably due to fertilization. The exoskeletons of all five specimens were hard. The spermatophoric mass, which is opaque-white, soft and jelly-like, is spread evenly over the entire surface of the last sternal plate of the thorax and extends anteriorly onto the preceding sternal plate, posteriorly onto the arthrodial mem brane of the abdomen, and laterally onto the coxopodites of the fifth pereiopods. It is roughly bilaterally symmetrical and the portions extruded from each gonopore of the male are clearly distinguishable as two rounded patches (PI. I). The seminal fluid within each vas deferens consists of a clear matrix in which is coiled a white tube-like spermatophore containing spermatozoa. This is typical of des criptions of the seminal fluid in other palinurid genera (Heydron, 1965). Micro scopic examination of the external spermatophoric mass, however, shows that the spermatozoa are spread diffusely throughout the jelly-like matrix. It appears, therefore, that the delicate spermatophores rupture when the spermatophoric mass is spread onto the sternum of the female, thus releasing the spermatozoa. In Panulirus the external spermatophores do not rupture and the spermatozoa remain localized within them. The thoracic sternum of the female lacks setae and the only apparent adaptation for attachment of the spermatophoric mass is the absence of a median tooth on the last sternal plate, thus making the surface flatter than in the preceding segments. The spermatophoric mass is sticky and adheres strongly to the sternum of the female.